ubuntu16.04一直报g++-5-multilib找不到是怎么回事啊？

Question

E: Unable to locate package 5:g++-5-multilib
E: Couldn't find any package by regex '5:g++-5-multilib'
You will have to install the above packages yourself.

我都已经安装了包g++-5-multilib

apt-cache search multilib

里面有这个包的，安装了还是提示